Institutional washing process using soil-release polymer

ABSTRACT

An institutional textile washing process comprising a washing step preceded by a pretreatment step comprising a soaking step or a prewash step, wherein the textile is treated in the pretreatment step in the presence of water with a soil release polymer comprising a copolyester of a dicarboxylic acid and a diol or a polydiol.

BACKGROUND OF THE INVENTION

This invention relates to an institutional washing process in which asoil release polymer is used in a separate pretreatment step.

Besides the ingredients essential to the washing process, such assurfactants and builders, detergents generally contain otherconstituents which may be collectively referred to as washingauxiliaries and which comprise such diverse groups of active substancesas foam regulators, redeposition inhibitors, bleaching agents, bleachactivators and dye transfer inhibitors. Auxiliaries of the type inquestion also include substances which provide the fibers withsoil-repellent properties and which, if present during the washingprocess, support the soil release capacity of the other detergentingredients. The same also applies to cleaning compositions for hardsurfaces. Substances such as these are often referred to as soil releaseagents or, by virtue of their ability to provide the treated surface,for example the fibers, with soil-repellent properties, as soilrepellents. By virtue of their chemical similarity to polyester fibers,copolyesters containing dicarboxylic acid units, alkylene glycol unitsand polyalkylene glycol units are particularly effective soil releaseagents. However, copolyesters are also capable of developing therequired effect in non-polyester fabrics. Soil release copolyesters ofthe type mentioned and their use in detergents have been known for sometime.

Thus, DE-OS 16 17 141 describes a washing process using polyethyleneterephthalate/polyoxyethylene glycol copolymers. DE-OS 22 00 911 relatesto detergents containing a nonionic surfactant and a copolymer ofpolyoxyethylene glycol and polyethylene terephthalate. DE-OS 22 53 063mentions acidic textile finishes containing a copolymer of a dibasiccarboxylic acid and an alkylene or cycloalkylene polyglycol and,optionally, an alkylene or cycloalkylene glycol. According to DE-OS 3324 258, ethylene terephthalate/polyethylene oxide terephthalate polymerswith molecular weights of 15,000 to 50,000, in which the polyethyleneglycol units have molecular weights of 1,000 to 10,000 and the molarratio of ethylene terephthalate to polyethylene oxide terephthalate is2:1 to 6:1, may be used in detergents. European patent EP 066 944relates to fabric treatment compositions containing a copolyester ofethylene glycol, polyethylene glycol, aromatic dicarboxylic acid andsulfonated aromatic dicarboxylic acid in certain molar ratios. Europeanpatent EP 185 427 mentions methyl-terminated or ethyl-terminatedpolyesters containing ethylene and/or propylene terephthalate andpolyethylene oxide terephthalate units and detergents containing thissoil release polymer. European patent EP 241 984 relates to polyesterswhich contain substituted ethylene units and glycerol units in additionto oxyethylene groups and terephthalic acid units. European patent EP241 985 discloses polyesters which, in addition to oxyethylene groupsand terephthalic acid units, contain 1,2-propylene, 1,2-butylene and/or3-methoxy-1,2-propylene groups and glycerol units and which areterminated by C₁₋₄ alkyl groups. European patent EP 253 567 relates tosoil release polymers with a molecular weight of 900 to 9,000 ofethylene terephthalate and polyethylene oxide terephthalate, thepolyethylene glycol units having molecular weights of 300 to 3,000 andthe molar ratio of ethylene terephthalate to polyethylene oxideterephthalate being 0.6 to 0.95:1. Polyesters containing polypropyleneterephthalate and polyoxyethylene terephthalate units which are at leastpartly terminated by C₁₋₄ alkyl or acyl groups are known from Europeanpatent application EP 272 033. European patent EP 274 907 describessulfoethyl-terminated terephthalate-containing soil release polyesters.According to European patent application EP 357 280, soil releasepolymers containing terephthalate, alkylene glycol and poly-C₂₋₄-glycolunits are prepared by sulfonation of unsaturated terminal groups.Polymers of ethylene terephthalate and polyethylene oxide terephthalate,in which the polyethylene glycol units have molecular weights of 750 to5,000 and the molar ratio of ethylene terephthalate to polyethyleneoxide terephthalate is 50:50 to 90:10 and their use in detergents isdescribed in German patent DE 28 57 292. German patent DE 28 46 984discloses certain hydrophilic polyurethanes and copolyesters containingrecurring alkoyl terephthalate and polyalkoyl terephthalate units andmixtures thereof as anti-soil detergent ingredients. Detergentscontaining 0.1 to 3% by weight of soil-releasing alkyl cellulose ethers,hydroxyalkyl cellulose ethers or hydroxyalkyl alkyl cellulose ethers aredescribed in German patent DE 26 13 791.

However, all the documents mentioned above relate to detergents fordomestic washing. The conditions typical of domestic washing, moreparticularly the action times of the wash liquor on the laundry to becleaned of at least 30 minutes and the relatively low alkalinity of thewashing liquor of, generally, well below pH 10, differ considerably fromthose typically prevailing in institutional laundries. Here, the totaltime taken by the laundry to pass through the continuous batch washingmachine with the treatment steps of wetting, prewashing, main washing,rinsing and optionally neutralization is only about 20 to 40 minutes, aperiod of only a few minutes being allocated for the actual washingprocess in the main wash zone. Another factor to be taken into accountis that, in institutional laundries, the washing is normally much moreheavily soiled than in the domestic sector. In order to obtain asatisfactory washing result under these conditions, washing ininstitutional laundries is normally carried out at far higher pH valuesthan washing in the home. Another difference in relation to domesticdetergents is that detergents for institutional washing often containneither bleaching agent nor bleach activator because, in institutionalwashing, bleaching and disinfection can be carried out in a separatestep, normally in one of the last zones before leaving the continuousbatch washing machine.

International patent application WO 96/24657 relates to a highlyalkaline detergent for use in institutional laundries which contains theabove-mentioned soil release polymer and which leads to a significantimprovement in cleaning performance when used in the main wash cycle ofinstitutional washing processes.

It has surprisingly been found that cleaning performance ininstitutional laundries can be distinctly improved if the soil releasepolymer, in addition to or instead of being used in the actualdetergent, is used in a separate pretreatment step.

Accordingly, the present invention relates to the use of soil releasepolymer in the soaking or prewash step of institutional washingprocesses.

The general principles of conventional institutional washing processesare described briefly in the following. A detailed account can be found,for example, in the article by H. Kräβmann and H. G. Hloch entitled“Waschverfahren in der Gewerblichen Wäscherei (Institutional WashingProcesses)”, Tenside Surfactants Detergents 24 (1987), 341-349 and theliterature cited therein.

Institutional washing processes differ from domestic washing processesinter alia in the fact that, although various types of fabrics anddifferently soiled fabrics have to be washed, the bulk of the laundrywithin the material sent for washing is normally the same so that awashing technique specially adapted to the particular cleaning functioncan be applied. However, there is a greater need for high-performancecleaning processes in institutional washing than in domestic washingbecause heavily soiled laundry, for example oil- and pigment-soiledworking apparel, can accumulate.

In order to keep the consumption of detergent as low as possible, thewater used for institutional washing is almost always free from hardnessions.

Whereas domestic washing is carried out almost exclusively inliquor-changing drum-type washing machines, various standard processesexist in institutional laundries. Thus, normal domestic washing withliquor-hanging washer-extractors can also be applied to theinstitutional sector. In these washer-extractors, the washing issuccessively exposed to various washing and rinsing conditions in adrum, the used liquor leaving the drum on completion of the particularwash phase. The individual steps are made up of soaking, prewashing,main washing, rinsing and spinning or pressing.

So-called continuous batch washing machines, which consist of severalsuccessive washing compartments or of a single washing compartmentdivided by partitions into several sections or chambers, are generallysuperior to this discontinuous process by virtue of the normally higherthroughput of laundry. In continuous batch washing machines, theindividual washing steps take place in various zones of the machinethrough which the laundry passes under program control. Continuous batchwashing machines can operate either on the bath-changing principle orwith stationary baths. Continuous batch washing machines generallyoperate on the countercurrent principle, fresh water and dirty washingbeing introduced into the washing process at opposite ends of thewashing machine and moving through the washing machine in more or lessopposite directions. Fresh water freed from hardness ions enters therinsing zone through which the laundry passes as the last zone in about1 to 10 minutes and from which part is delivered to the main wash zone.Another part of the water emanating from the rinsing zone is often used,together with the water accumulating in the pressing zone of thecontinuous batch washing machine, for the first step of the washingprocess, namely wetting of the dry soiled laundry and introduction intothe first bath of the continuous batch washing machine. After automaticaddition of one or more detergents, the soiled laundry is normallyprewashed at 35 to 45° C. and, after a predetermined time, isautomatically further transported. The prewash step may also be carriedout in several successive units. The used water normally leaves thecontinuous batch washing machine at the end of the prewash zone. Afterleaving the prewash zone, the laundry enters the main wash zone whichgenerally consists of several units, often more than ten in number.Because the countercurrent of the water flow is superimposed on theintermittent co-current emanating from transport of the laundry, whichresults in complicated concentration conditions, the main wash detergentis generally not added in the first unit, but in one of the middleunits. Bleaching agents, for example hydrogen peroxide or peraceticacid, are normally added in this zone. Also in this zone, the laundry isautomatically further transported into the next unit, normally afterfreely programmable cycle times. In the course of the final rinsingstep, the laundry is normally neutralized (“acidified”) by automaticallydosed addition of organic acids to the aqueous rinsing solution.Neutralization is essential on account of the use of soft water inconjunction with the alkaline cleaning baths of the main washing step.

DESCRIPTION OF THE INVENTION

The modification according to the invention of these known processes forthe institutional washing of laundry essentially comprises treating thetextiles to be washed with the soil release polymer in the presence ofwater before the main washing step, i.e. in the soaking or prewashphase. Treatment times of 5 minutes to 60 minutes and, moreparticularly, 10 minutes to 40 minutes at temperatures of 30° C. to 90°C. and, more particularly, 30° C. to 60° C. are normally quitesufficient. The soil release polymer is used in quantities of normally0.1 g to 100 g, preferably 1 g to 20 g and more preferably 1 g to 10 gper kg of dry laundry. The liquor ratio, i.e. the ratio of the weight ofdry laundry to be washed to the quantity of water containing soilrelease polymer, is preferably in the range from 1:3 to 1:30 and morepreferably in the range from 1:5 to 1:10.

Suitable soil release polymers for the purposes of the invention are, inparticular, copolyesters of dicarboxylic acids, for example adipic acid,phthalic acid or terephthalic acid, diols, for example ethylene glycolor propylene glycol, and polydiols, for example polyethylene glycol orpolypropylene glycol, and nonionic hydroxyalkyl cellulose ethers, forexample hydroxypropyl cellulose.

Suitable soil release polyesters are known from the documents citedabove and from German patent applications DE 44 17 686 and DE 195 02 181and are commercially obtainable, for example, under the names ofSokalan® (BASF) and Velvetol® 251C (Rhône Poulenc). Preferred soilrelease polyesters include compounds which, formally, can be obtained byesterifying two monomers, the first monomer being a dicarboxylic acidHOOC—Ph—COOH and the second monomer being a diol H—(O—(CHR³—)_(a)OH,which may also be present as polymeric diol H—(O—(CHR³—)_(a))_(b)OH. Inthese formulae, Ph represents an o-, m- or p-phenylene group which maycarry 1 to 4 substituents selected from C₁₋₂₂ alkyl groups, sulfonicacid groups, carboxyl groups and mixtures thereof, R³ is hydrogen, aC₁₋₂₂ alkyl group or mixtures thereof, a is a number of 2 to 6 and b isa number of 1 to 300. The polyesters obtainable from these monomerspreferably contain both monomer diol units O—(CHR³—)_(a)O— and polymerdiol units —(O—(CHR³—)_(a))_(b)O—. The molar ratio of monomer diol unitsto polymer diol units is preferably 100:1 to 1:100 and, more preferably,10:1 to 1:10. In the polymer diol units, the degree of polymerization bis preferably in the range from 4 to 200 and more preferably in therange from 12 to 140. The molar weight or rather the average molecularweight or the maximum of the molecular weight distribution of preferredsoil release polyesters is in the range from 250 to 100,000 and morepreferably in the range from 500 to 50,000. The acid on which the groupPh is based is preferably selected from terephthalic acid, isophthalicacid, phthalic acid, trimellitic acid, mellitic acid, the isomers ofsulfophthalic acid, sulfoisophthalic acid and sulfoterephthalic acid andmixtures thereof. If their acid groups are not part of the ester bondsin the polymer, they are preferably present in salt form, moreparticularly as alkali metal or ammonium salts. Of these, the sodium andpotassium salts are particularly preferred. If desired, all of themonomer HOOC—Ph—COOH or, more particularly, no more than 10 mole-%,based on the percentage content of Ph with the meaning defined above,may be replaced by other acids containing at least two carboxyl groupsin the soil release polyester. These acids include, for example,alkylene and alkenylene dicarboxylic acids, such as malonic acid,succinic acid, fumaric acid, maleic acid, glutaric acid, adipic acid,pimelic acid, suberic acid, azelaic acid and sebacic acid. The preferreddiols HO—(CHR³—)_(a)OH include those in which R³ is hydrogen and a is anumber of 2 to 6 and those in which a has a value of 2 and R³ isselected from hydrogen and alkyl groups containing 1 to 10 and, moreparticularly, 1 to 3 carbon atoms. Among the last-mentioned diols, thosewith the formula HO—CH₂CHR³—OH, where R³ is as defined above, areparticularly preferred. Examples of diol components are ethylene glycol,1,2-propylene glycol, 1,3-propylene glycol, butane-1,4-diol,pentane-1,5-diol, hexane-1,6-diol, octane-1,8-diol, decane-1,2-diol,dodecane-1,2-diol and neopentyl glycol. Among the polymeric diols,polyethylene glycol with an average molecular weight of 1,000 to 6,000is particularly preferred.

If desired, the polyesters having the composition described above mayalso be end-capped, suitable terminal groups being alkyl groupscontaining 1 to 22 carbon atoms and esters of monocarboxylic acids. Theterminal groups attached via ester bonds may be based on alkyl, alkenyland aryl monocarboxylic acids containing 5 to 32 carbon atoms and, moreparticularly, 5 to 18 carbon atoms. These include valeric acid, caproicacid, oenanthic acid, caprylic acid, pelargonic acid, capric acid,undecanoic acid, undecenoic acid, lauric acid, lauroleic acid,tridecanoic acid, myristic acid, myristoleic acid, pentadecanoic acid,palmitic acid, stearic acid, petroselic acid, petroselaidic acid, oleicacid, linoleic acid, linolaidic acid, linolenic acid, elaeostearic acid,arachic acid, gadoleic acid, arachidonic acid, behenic acid, erucicacid, brassidic acid, clupanodonic acid, lignoceric acid, cerotic acid,melissic acid, benzoic acid which may contain 1 to 5 substituents with atotal of up to 25 carbon atoms, more particularly 1 to 12 carbon atoms,for example tert.butyl benzoic acid. The terminal groups may also bebased on hydroxymonocarboxylic acids containing 5 to 22 carbon atomswhich include, for example, hydroxyvaleric acid, hydroxycaproic acid,ricinoleic acid, the hydrogenation product thereof, hydroxystearic acidand o-, m- and p-hydroxybenzoic acid. The hydroxymonocarboxylic acidsmay in turn be attached to one another by their hydroxyl group and theircarboxyl group and, accordingly, may occur repeatedly in one and thesame terminal group. The number of hydroxymonocarboxylic acid units perterminal group, i.e. their degree of oligomerization, is preferably inthe range from 1 to 50 and, more preferably, in the range from 1 to 10.

A preferred embodiment of the invention is characterized by the use ofpolymers of ethylene terephthalate and polyethylene oxide terephthalatein which the polyethylene glycol units have molecular weights of 750 to5,000 and the molar ratio of ethylene terephthalate to polyethyleneoxide terephthalate is 50:50 to 90:10.

Nonionic hydroxyalkyl cellulose ethers suitable for use as soil releasepolymers in accordance with the invention include in particularhydroxyethyl, hydroxypropyl and/or hydroxybutyl celluloses which mayadditionally carry alkyl ether groups, more particularly, methyl, ethyland/or propyl groups. Their content of hydroxyalkoxy groups ispreferably from 1% by weight to 20% by weight, more preferably from 2%by weight to 15% by weight and most preferably from 5% by weight to 10%by weight, based on nonionic hydroxyalkyl cellulose ether. If additionalalkoxy groups are present, their content is preferably from 15% byweight to 30% by weight and, more preferably, from 20% by weight to 30%by weight, based on nonionic hydroxyalkyl cellulose ether. Anioniccellulose ethers, for example carboxymethyl cellulose, are significantlyless effective than nonionic cellulose ethers. Preferred nonioniccellulose ethers include alkyl hydroxyalkyl celluloses, for examplemethyl hydroxyethyl cellulose, methyl hydroxypropyl cellulose, methylhydroxybutyl cellulose, ethyl hydroxyethyl cellulose, ethylhydroxypropyl cellulose and/or ethyl hydroxybutyl cellulose.

Another preferred embodiment of the invention is characterized by theuse of combinations of the esters mentioned above with the nonioniccellulose ethers mentioned above in quantity ratios of, preferably, 1:1to 1:10 and, more preferably, 1:1 to 1:5. If nonionic cellulose ether isused as the soil release polymer, it may be present in the form of, forexample, a solid mixture of the cellulose ether with up to about 10% byweight of sodium chloride and about 6% by weight to 8% by weight ofwater without any adverse effect on the improvement in oil and fatremoval.

Both in the use according to the invention and in the process accordingto the invention, the soil release polymer may be used either on its ownor as part of a presoak or prewash composition which may contain all theother ingredients typical of such compositions, including for examplenonionic surfactants, enzymes, phosphates and silicates and alsopolymeric polycarboxylates.

After the treatment according to the invention with the soil releasepolymer, the laundry is subjected to the washing process, preferablywithout preliminary rinsing, using the standard methods mentioned aboveor methods based thereon.

EXAMPLES

In a Frista® machine, the fabrics listed in the following Table werepretreated (30 minutes, 30° C., no rinsing out) with a 1:1 mixture ofmethyl hydroxypropyl cellulose and a polymer of ethylene terephthalateand polyethylene oxide terephthalate (Velvetol®, a product of RhônePoulenc) in a quantity of 3 g per kg of dry laundry, subsequentlyprovided with the soils listed in Table 1, washed with a standarddetergent (Silex perfect®) in an E-Lux® washing machine (5 minutes 30°C., 50 minutes 60° C.; water hardness 0° dH) and dried. The cycle thenbegan again, the soils being applied to the same places in order tosimulate repeated use. All the fabrics were washed 6 times (process I).

In a modification of this procedure, the pretreatment was only carriedout after every third wash and not after every wash (process II).

For comparison, the pretreatment with the soil release polymer wasomitted altogether (process III).

The test fabrics were then dried and evaluated by a panel of 5 examinersfor cleanness or rather freedom from stains on a scale of 0 to 3 where

0=complete stain removal

1=slight residues

2=distinctly visible residues

3=almost as starting value

The average values of the individual evaluations are set out in Table 1.It can be seen that significantly better cleaning results are obtainedin the process according to the invention (process I and process II)than in conventional washing processes (process III). Comparable resultswere obtained when the mixture of methyl hydroxypropyl cellulose and apolymer of ethylene terephthalate and a polyethylene oxide terephthalatewas replaced by the polymer as sole soil release agent.

TABLE 1 Evaluation of washing performance Soil/fabric Process I ProcessII Process III A 2 3 3 B 2 2 2 C 2 2 2 D 0 1 2 E 1 1 1 F 1 2 2 Average1.3 1.8 2.0 Soil/fabric: A used engine oil on polyester B used engineoil on cotton C used engine oil on cotton/polyester blend D mixture ofdust/sebum paste with engine oil on polyester E mixture of dust/sebumpaste with engine oil on cotton F mixture of dust/sebum paste withengine oil on cotton/polyester blend

What is claimed is:
 1. An institutional textile washing processcomprising a washing step preceded by a pretreatment step comprising asoaking step or a prewash step, wherein the textile is treated in thepretreatment step in the presence of water with a soil release polymercomprising a copolyester of a dicarboxylic acid and a diol or apolydiol.
 2. A process according to claim 1, wherein the polyester is acopolymer of ethylene terephthalate and polyethyleneoxide terephthalate,wherein the polyethylene glycol units have a molecular weight of 750 to5000 and the molar ratio of ethylene terephthalate to polyethyleneoxideterephthalate is 50:50 to 90:10.
 3. A process according to claim 1,wherein the soil release polymer is combination of the polyester and anonionic hydroxyalkyl cellulose ether in a weight ratio of 1:1 to 1:10.4. A process according to claim 3, wherein the soil release polymer iscombination of the polyester and the nonionic hydroxyalkyl celluloseether in a weight ratio of 1:1 to 1:5.
 5. A process according to claim1, wherein the treatment time with the soil release polymer is 5 to 60minutes.
 6. A process according to claim 5, wherein the treatment timewith the soil release polymer is 10 to 40 minutes.
 7. A processaccording to claim 1, wherein the treatment with the soil releasepolymer is carried out a a temperature of 30° C. to 90° C.
 8. A processaccording to claim 7, wherein the treatment with the soil releasepolymer is carried out a a temperature of 30° C. to 60° C.
 9. A processaccording to claim 1, wherein the textile is treated with 0.1 to 100grams of soil release polymer per kilogram of dry textile.
 10. A processaccording to claim 9, wherein the textile is treated with 1 to 10 gramsof soil release polymer per kilogram of dry textile.
 11. A processaccording to claim 1, wherein the pretreatment step in which the textileis treated with the soil release polymer has a liquor ratio of 1:3 to1:30.
 12. A process according to claim 1, wherein the pretreatment stepin which the textile is treated with the soil release polymer has aliquor ratio of 1:5 to 1:10.
 13. An institutional textile washingprocess comprising a washing step preceded by a pretreatment stepcomprising a soaking step or a prewash step, wherein the textile intreated in the pretreatment step in the presence of water with a soilrelease polymer comprising a copolyester of ethylene terephthalate andpolyethyleneoxide terephthalate, wherein the polyethylene glycol unitshave a molecular weight of 750 to 5000 and the molar ratio of ethyleneterephthalate to polyethyleneoxide terephthalate is 50:50 to 90:10,wherein the treatment with the soil release polymer is carried out for 5to 60 minutes at a temperature of 30° C. to 90° C. using 0.1 to 100grams of soil release polymer per kilogram or dry textile at a liquorratio of 1:3 to 1:30.
 14. A process according to claim 13, wherein thetreatment with the soil release polymer is carried out for 10 to 40minutes at a temperature of 30° C. to 60° C. using 1 to 10 grams of soilrelease polymer per kilogram of dry textile at a liquor ratio of 1:5 to1:10.